U.S. patent number 5,132,368 [Application Number 07/758,425] was granted by the patent office on 1992-07-21 for fluoropolymer process aids containing functional groups.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to George R. Chapman, Jr., Donnan E. Priester, Charles W. Stewart, Robert E. Tarney.
United States Patent |
5,132,368 |
Chapman, Jr. , et
al. |
July 21, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Fluoropolymer process aids containing functional groups
Abstract
The subject invention provides a composition having excellent
extrusion characteristics comprising a difficulty-melt-processible
polymer and 0.002-0.5 wt. % of one or more fluoropolymer process
aids wherein the fluoropolymer has a fluorine to carbon ratio of at
least 1:2, is capable of forming a die-coating film under the
prevailing conditions of extrusion temperature and pressure, and
contains an effective amount of polar functional polymer chain end
groups, --W, wherein --W is selected from --COF, --SO.sub.2 F,
--SO.sub.3 M, --OSO.sub.3 M, --COOR, and --COOM, wherein R is
C.sub.1-3 alkyl and M is hydrogen, a metal cation, preferably an
alkali or alkaline earth metal cation, or a quaternary ammonium
cation.
Inventors: |
Chapman, Jr.; George R. (Media,
PA), Priester; Donnan E. (Wilmington, DE), Stewart;
Charles W. (Newark, DE), Tarney; Robert E. (Hockessin,
DE) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
27411183 |
Appl.
No.: |
07/758,425 |
Filed: |
September 3, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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572922 |
Aug 29, 1990 |
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418376 |
Oct 6, 1989 |
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461093 |
Jan 4, 1990 |
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216421 |
Jul 8, 1988 |
4904735 |
Feb 27, 1990 |
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Current U.S.
Class: |
525/165; 525/166;
525/176; 525/179; 525/183; 525/200; 525/72; 525/175; 525/178;
525/182; 525/199 |
Current CPC
Class: |
C08L
23/02 (20130101); B29C 48/272 (20190201); C08L
67/00 (20130101); C08L 77/00 (20130101); C08L
101/00 (20130101); C08L 25/06 (20130101); C08L
23/02 (20130101); C08L 25/06 (20130101); C08L
67/00 (20130101); C08L 77/00 (20130101); C08L
101/00 (20130101); C08L 27/12 (20130101); B29C
48/03 (20190201); C08L 2666/04 (20130101); C08L
2666/04 (20130101); C08L 2666/04 (20130101); C08L
2666/04 (20130101); C08L 2666/04 (20130101) |
Current International
Class: |
C08L
25/00 (20060101); C08L 25/06 (20060101); C08L
67/00 (20060101); C08L 77/00 (20060101); C08L
23/02 (20060101); C08L 101/00 (20060101); C08L
23/00 (20060101); C08L 27/12 (20060101); C08L
27/00 (20060101); C08L 027/12 (); C08L 023/02 ();
C08L 077/00 (); C08L 067/00 () |
Field of
Search: |
;525/165,175,176,178,183,199,200 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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59-113059 |
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Jun 1984 |
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JP |
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63-55543 |
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Nov 1988 |
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JP |
|
Primary Examiner: Seccuro; Carman J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No.
07/572,922 filed Aug. 29, 1990, now abandoned, which is a
continuation-in-part of application Serial No. 07/418,376 filed
Oct. 6, 1989 and of application Ser. No. 07/461,093 filed Jan. 4,
1990 as a continuation-in-part of application Ser. No. 07/216,421
filed Jul. 8, 1988 and issued Feb. 27, 1990 as U.S. Pat. No.
4,904,735. Application Ser. No. 07/461,093 was allowed Jun. 1,
1990. Application Ser. No. 07/418,376 was abandoned after the
filing of application Ser. No. 572,922 and application Ser. No.
07/461,093 was abandoned after the filing of continuation-in-part
application Ser. No. 07/572,921 which was allowed and issued May 7,
1991 as U.S. Pat. No. 5,013,792.
Claims
We claim:
1. Composition comprising a difficultly-melt-processible polymer
and 0.002-0.5 wt. % of a fluoropolymer process aid that:
(a) has a fluorine to carbon ratio of at least 1:1.5,
(b) has polymer chain ends bearing a functional group, W, wherein W
is selected from --COF, --SO.sub.2 F, SO.sub.3 M, --OSO.sub.3 M,
--COOR and COOM, wherein R is a C.sub.1-3 alkyl group and M is
hydrogen, a metal cation or a quaternary ammonium cation,
(c) is selected from the group consisting of
(i) an irradiated polytetrafluoroethylene,
(ii) a partially crystalline copolymer of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether) or a perfluoroolefin containing 3-8
carbon atoms,
(iii) an elastomeric copolymer of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether),
(iv) a copolymer of tetrafluoroethylene and 0.5-40 mole % of a
functional-group-containing monomer ##STR3## wherein Z is --F or
--CF.sub.3, x is 0 or an integer of 1-4, y is 0 or 1, z is an
integer of 1-12, and W' is selected from --SO.sub.2 F, --SO.sub.2
C1, --SO.sub.3 H, --COOR or --COOM, wherein R is C.sub.1-3 alkyl
and M is hydrogen, a metal cation, or a quaternary ammonium cation,
and
(d) contains at least 100 functional groups W per million carbon
atoms.
2. Composition of claim 1 wherein, in W, the metal cation is an
alkali metal or alkaline earth metal cation and, in W', the metal
cation is an alkali metal cation.
3. Composition of claim 1 wherein the difficultly-melt-processible
polymer is selected from mono-olefin polymers; vinyl aromatic
polymers; copolymers of alpha-olefins and vinyl esters,
(meth)acrylic esters, (meth)acrylic acids and their (ionomeric)
metal salts or acrylonitrile; chlorinated polyethylene; polyvinyl
chloride; polyamide; and polyester.
4. Composition of claim 3 wherein the difficultly-melt-processible
polymer is a polyester.
5. Composition of claim 3 wherein the difficultly-melt-processible
polymer is a polyamide.
6. Composition of claim 3 wherein the difficultly-melt-processible
polymer is a copolymer of ethylene and vinyl acetate.
7. Composition of claim 3 wherein the difficultly-melt-processible
polymer is a polystyrene.
8. Composition of claim 3 wherein the difficultly-melt-processible
polymer is a hydrocarbon mono-olefin polymer.
9. The composition of claim 8 wherein the hydrocarbon polymer is a
homopolymer or copolymer of one or more monoolefins of the formula
RCH.dbd.CH.sub.2 wherein R is H or alkyl.
10. The composition of claim 9 wherein alkyl is C.sub.1-8
alkyl.
11. The composition of claim 8 wherein the hydrocarbon polymer is
low density polyethylene.
12. The composition of claim 8 wherein the hydrocarbon polymer is
linear low density polyethylene.
13. The composition of claim 8 wherein the hydrocarbon polymer is
high density polyethylene.
14. The composition of claim 8 wherein the hydrocarbon polymer is a
copolymer of ethylene, propylene and a non-conjugated diene.
15. The composition of claim 1 wherein W is --SO.sub.3 H.
16. The composition of claim 1 wherein W is --COF.
17. The composition of claim 1 wherein W is --COOH.
18. The composition of claim 1 wherein the fluoropolymer is a
partially crystalline copolymer of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether).
19. The composition of claim 18 wherein the alkyl group is
propyl.
20. The composition of claim 1 wherein the fluoropolymer is
(c)(iii).
21. The composition of claim 20 wherein the alkyl group is
methyl.
22. The composition of claim 1 wherein the fluoropolymer is a
partially crystalline copolymer of tetrafluoroethylene and a
perfluoroolefin containing 3-8 carbon atoms.
23. The composition of claim 22 wherein the perfluoroolefin is
hexafluoropropylene.
24. The composition of claim 1 wherein the fluoropolymer is
polytetrafluoroethylene that has been treated with 15-80 megarads
of ionizing radiation and W is --COF.
25. The composition of claim 1 wherein the fluoropolymer is
polytetrafluoroethylene that has been treated with 15-80 megarads
of ionizing radiation and W is --COOH.
26. The composition of claim 1 wherein the fluoropolymer is (c)
(IV).
27. The composition of claim 26 wherein the fluoropolymer is a
copolymer of tetrafluoroethylene and
perfluoro-3,6-dioxa-4-methyl-7-octene sulfonic acid.
28. The composition of claim 26 wherein the fluoropolymer is a
copolymer of tetrafluoroethylene and methyl
perfluoro(4,7-dioxa-5-methyl-8-noneneoate).
29. The composition of claim 26 wherein the fluoropolymer is a
copolymer of tetrafluoroethylene and
perfluoro-3,6-dioxa-4-methyl-7-octene sulfonyl fluoride.
30. The composition of claim 26 wherein the fluoropolymer is a
copolymer of tetrafluoroethylene and
perfluoro-4,7-dioxa-5-methyl-8-nonenoic acid.
31. The composition of claim 1 comprising a blend of
difficultly-melt-processible polymers.
32. The composition of claim 1 wherein the
difficultly-melt-processible polymer is a polymeric alloy.
33. The composition of claim 32, wherein the alloy is comprised of
a polyamide 6/6, an ethylene/n-butyl acrylate/methacrylic acid
copolymer and an ethylene/n-butyl acrylate/glycidyl methacrylate
copolymer.
34. Composition comprised of linear low density polyethylene and
0.002-0.5 wt. % of a partially crystalline copolymer of
tetrafluoroethylene and hexafluoropropylene having at least 200
--COF and --COOH groups per million carbon atoms.
35. Composition comprising linear low density polyethylene and
0.002-0.5 wt. % of polytetrafluoroethylene that has been treated
with ionizing radiation sufficient to provide at least 200 --COF
and --COOH groups per million carbon atoms.
36. Process comprising melt extruding a
difficultly-melt-processible polymer having incorporated therein an
effective amount, to improve processibility, of a fluoropolymer
process aid that:
(a) has a fluorine to carbon ratio of at least 1:1.5,
(b) has polymer chain ends bearing a functional group, W, wherein W
is selected from --COF, --SO.sub.2 F, SO.sub.3 M, --OSO.sub.3 M,
--COOR and COOM, wherein R is a C.sub.1-3 alkyl group and M is
hydrogen, a metal cation or a quaternary ammonium cation,
(c) is selected from the group consisting of
(i) an irradiated polytetrafluoroethylene,
(ii) a partially crystalline copolymer of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether) or a perfluoroolefin containing 3-8
carbon atoms,
(iii) an elastomeric copolymer of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether),
(iv) a copolymer of tetrafluoroethylene and 0.5-40 mole % of a
functional-group-containing monomer ##STR4## wherein Z is --F or
--CF.sub.3, x is 0 or an integer of 1-4, y is 0 or 1, z is an
integer of 1-12, and W, is selected from --SO.sub.2 F, --SO.sub.2
C1, --SO.sub.3 H, --COOR or --COOM, wherein R is C.sub.1-3 alkyl
and M is hydrogen, a metal cation, or a quaternary ammonium cation,
and
(d) contains at least 100 functional groups W per million carbon
atoms.
37. Process of claim 36 wherein the concentration of fluoropolymer
is 0.002-0.5 wt. %, based on the difficultly-melt-processible
polymer.
38. Process of claim 36 wherein the difficultly-melt-processible
polymer is a polyester.
39. Process of claim 36 wherein the difficultly-melt-processible
polymer is a polyamide.
40. Process of claim 36 wherein the difficultly-melt-processible
polymer is a copolymer of ethylene and vinyl acetate.
41. Process of claim 36 wherein the difficultly-melt-processible
polymer is a polystyrene.
42. Process of claim 36 wherein the difficultly-melt-processible
polymer is a hydrocarbon mono-olefin polymer.
43. The process of claim 42 wherein the hydrocarbon polymer is
linear low density polyethylene and the fluoropolymer is a
partially crystalline copolymer of tetrafluoroethylene and
hexafluoropropylene, has at least 200 --COF and --COOH groups per
million carbon atoms and is present in an amount of 0.005-0.5 wt.
%, based on the hydrocarbon polymer.
44. The process of claim 42 wherein the hydrocarbon polymer is
linear low density polyethylene and the fluoropolymer is a
polytetrafluoroethylene that has been treated with ionizing
radiation sufficient to provide at least 200 --COF and --COOH
groups per million carbon atoms and is present in an amount of
0.005-0.5 wt. %, based on the hydrocarbon polymer.
45. Process of claim 36 wherein W is --SO.sub.3 H.
46. Process of claim 36 wherein W is --COF.
47. Process of claim 36 wherein W is --COOH.
48. Process of claim 36 wherein the fluoropolymer is a partially
crystalline copolymer of tetrafluoroethylene and a perfluoro(alkyl
vinyl ether).
49. Process of claim 48 wherein the alkyl group is propyl.
50. Process of claim 36 wherein the fluoropolymer is (c)(iii).
51. Process of claim 50 wherein the alkyl group is methyl.
52. Process of claim 36 wherein the fluoropolymer is a partially
crystalline copolymer of tetrafluoroethylene and a perfluoroolefin
containing 3-8 carbon atoms.
53. Process of claim 52 wherein the perfluoroolefin is
hexafluoropropylene.
54. Process of claim 36 wherein the fluoropolymer is
polytetrafluoroethylene that has been treated with 15-80 megarads
of ionizing radiation and W is --COF.
55. Process of claim 36 wherein the fluoropolymer is
polytetrafluoroethylene that has been treated with 15-80 megarads
of ionizing radiation and W is --COOH.
56. Process of claim 36 wherein the fluoropolymer is (c) (iv).
57. Process of claim 56 wherein the fluoropolymer is a copolymer of
tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octene
sulfonic acid.
58. Process of claim 56 wherein the fluoropolymer is a copolymer of
tetrafluoroethylene and methyl
perfluoro(4,7-dioxa-5-methyl-8-noneneoate).
59. Process of claim 56 wherein the fluoropolymer is a copolymer of
tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octene
sulfonyl fluoride.
60. Process of claim 56 wherein the fluoropolymer is a copolymer of
tetrafluoroethylene and perfluoro-4,7-dioxa-5-methyl-8-nonenoic
acid.
61. Process of claim 36 wherein the difficultly-melt-processible
polymer has incorporated therein a mixture of process aids.
62. Process of claim 36 wherein the difficultly-melt-processible
polymer is comprised of a mixture of such polymers.
63. Process of claim 36 wherein the difficultly-melt-processible
polymer is a polymeric alloy.
64. Process of claim 63 wherein the alloy is comprised of a
polyamide 6/6, an ethylene/n-butyl acrylate/methacrylic acid
copolymer and an ethylene/n-butyl acrylate/glycidyl methacrylate
copolymer.
65. Composition of claim 1 wherein the concentration of
fluoropolymer process aid is 0.01-0.2 wt. %, based on the
difficultly-melt-processible polymer.
66. Composition of claim 34 wherein the concentration of the
partially crystalline copolymer is 0.01-0.2 wt. %, based on the
polyethylene.
67. Composition of claim 35 wherein the concentration of the
treated polytetrafluoroethylene is 0.01-0.2 wt. %, based on the
polyethylene.
68. Process of claim 36 wherein the concentration of fluoropolymer
is 0.01-0.2 wt. %, based on the difficultly-melt-processible
polymer.
69. The composition of claim 1 comprising a mixture of
fluoropolymer process aids.
70. The process of claim 36 wherein a mixture of fluoropolymer
process aids is incorporated into the difficultly-melt-processible
polymer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved process aid compositions for the
melt extrusion of difficultly-melt-processible polymers.
2. Background
In the melt extrusion of polymer resins there are often flow
regimes, determined by the rheological properties of the particular
resin, where anomalous flow behavior occurs leading to surface
imperfections on the extrudate surfaces. Such imperfections,
commonly called melt fracture, appear in different forms. The
so-called "sharkskin" fracture occurs at lower shear rates and
appears as a general, finely-structured and uniform roughness. In a
blown-film extrusion sharkskin fracture may appear as an
undesirable herringbone pattern, reducing clarity and giving a dull
surface. In practice this may occur at uneconomically low extrusion
rates. At higher shear rates flow often becomes unstable and a
non-uniform stick-slip melt fracture results, wherein alternating
bands of glossy surface and sharkskin fracture appear. This
behavior is especially undesirable in wire coating and in tube and
pipe extrusions as well as in blown-film applications. Other
well-known problems that create difficulties in extrusion include
fluctuations in barrel and die pressure, torquing out because of
the excessively high pressure reached during a fluctuation, and
accumulation of degraded polymer at the die exit orifice.
In an effort to improve the extrusion behavior of polymer resins
through metal dies it is known to coat the die surfaces that
contact the flowing polymer melt with a slip agent, such as
tetrafluoroethylene polymers and copolymers, as in Japanese
Application Publication Kokai 55-82784 (Mitsui Petrochem. Ind.,
KK), but bonding to the metal is poor, and over a period of time in
use the slip layer is depleted and melt fracture resumes.
In other practices, as for example in the extrusion of certain
hydrocarbon polymers and copolymers, it is known to employ small
amounts of fluorocarbon polymers, blended with the extrusion resin,
as a continuously replenishing slip agent. Thus Blatz, in U.S. Pat.
No. 3,125,547, discloses hydrocarbon polymer compositions having
improved extrusion behavior that contain small amounts of
fluorocarbon polymers that are above their glass transition
temperature, if amorphous, or above their crystalline melting point
(e.g. molten), if crystalline, at the process temperatures. Under
these conditions the flow rate above which melt fracture occurs is
greatly increased, and required extrusion pressures for a given
extrusion rate are diminished. Takeshi and Inui in Japanese
Examined Application Kokoku 70-30574 disclose continuous extrusion
molding of polyethylene compositions containing small amounts of
tetrafluoroethylene polymer (crystalline at process temperatures).
Japanese Unexamined Application Kokai 1,074,247 describes the use
of certain combinations of fluoropolymer process aids disclosed in
U.S. Pat. No. 3,125,547, cited above. U.S. Pat. No. 4,904,735
discloses the use of combinations of fluoropolymers that are molten
at process temperatures, such as fluoroelastomers, and those that
are not molten at process temperatures, such as crystalline
tetrafluoroethylene homopolymers and copolymers.
Japanese Examined Applications Kokoku 55543/1988 and 55544/1988
describe compositions comprising a thermoplastic resin and a
fluoropolymer process aid having pendant --SO.sub.3 M groups, where
M is an alkali metal anion.
The important effect of polar functionality situated on the
fluoropolymer chain has not been heretofore recognized. It is an
objective of this invention to describe fluoropolymer compositions
having effective concentrations of polar functionality and enhanced
utility as process aids for the extrusion of
difficultly-melt-processible polymers.
SUMMARY OF THE INVENTION
The invention herein provides a composition having excellent
extrusion characteristics. The composition comprises a
difficultly-melt-processible polymer and 0.002-0.5 wt. %,
preferably 0.01-0.2 wt. %, of one or more fluoropolymers wherein
the fluoropolymer has a fluorine to carbon ratio of at least 1:2,
preferably at least 1:1.5, and has chain ends bearing one or more
functional groups W, wherein W is selected from --COF, --SO.sub.2
F, --SO.sub.3 M, --OSO.sub.3 M, --COOR and --COOM, wherein R is a
C.sub.1-3 alkyl group and M is hydrogen, a metal cation, preferably
an alkali or alkaline earth metal cation, or a quaternary ammonium
cation. More specifically, the fluoropolymer is selected from the
group consisting of (i) irradiated polytetrafluoroethylene, (ii) a
partially crystalline copolymer of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether) or a perfluoroolefin containing 3-8
carbon atoms, (iii) an elastomeric copolymer of tetrafluoroethylene
and a perfluoro(alkyl vinyl ether, (iv) a copolymer of vinylidene
fluoride, hexafluoropropylene and tetrafluoroethylene and (v) a
copolymer of one or more fluoroolefins and 0.5-40 mole % of a
functional-group-containing monomer ##STR1## wherein Z is --F or
--CF.sub.3, x is 0 or an integer of 1-4, y is 0 or 1, z is an
integer of 1-12, and W' is selected from the functional groups
--SO.sub.2 F, --SO.sub.2 C1, --SO.sub.3 H, --COOR or --COOM,
wherein R is C.sub.1-3 alkyl and M is hydrogen, a metal cation,
preferably an alkali metal cation, or a quaternary ammonium cation,
said fluoropolymer containing at least 100 functional groups W per
million carbon atoms.
The end-group functionality, W, can be introduced into the
fluoropolymer process aid, for example: (1) as polymer chain end
groups during polymerization, or (2) by subjecting polymer without
the end groups to ionizing radiation.
BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1-7 are plots of extrusion die pressure (MPa) vs. throughput
(g/minute) of difficulty-melt-processible polymers, with and
without process aids of the invention, as demonstrated in the
examples provided hereinafter. More specifically, FIGS. 1-4 are
representative of the invention as applied to a
difficultly-melt-processible linear low density polyethylene, as
described in Examples 1-8 and Comparative Examples 1 and 3. FIG. 5
is similarly representative for polystyrene, as described in
Example 9. FIG. 6 is similarly representative for an ethylene/vinyl
acetate copolymer, as described in Example 10. FIG. 7 is similarly
representative for a polyamide, as described in Example 13.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to fluoropolymers having utility in
improving the extrusion behavior of difficultly-melt-processible
polymer resins.
The term "extrusion behavior" used herein is intended to include,
individually or in combination, such parameters as the die pressure
reached during extrusion and the resultant power requirements, the
operating melt temperatures required, and the maximum extrusion
rates that can be achieved while maintaining melt stability and
good extrudate surface quality.
Still further examples of poor extrusion behavior which may be
overcome by means of this invention include the formation of
deposits of extruding polymer resin, decomposed polymer and/or
components of the resin around the die exit (orifice); uneven
pumping of the polymer melt, resulting in fluctuations in pressure
and output and a resulting surging of the polymer melt; and
torquing out of the extruder, that is, automatic shutting down of
the extruder because of the high pressure buildup, exceeding safety
limits, during peaks of pressure surges.
Yet another measure of "extrusion behavior" resides in the
efficient use of the fluoropolmer process aid, that is in the
amount that may be required for noticeable and economically useful
improvement in extrusion properties to be observed.
Difficultly-melt-processible polymers are defined as those that
require uneconomically high extrusion pressures (high power
requirement) or temperatures for extrusion; that extrude with
unacceptable melt fracture, such that the surfaces of the extrudate
are blemished under conditions that would be otherwise technically
feasible or economically attractive; or that otherwise show poor
extrusion behavior such as described above.
A number of critical requirements must be met for the fluoropolymer
process aids of this invention to function well. The fluoropolymer
must be incompatible in the difficultly-melt-processible resin. In
addition, the fluoropolymer must disperse, and remain dispersed, in
the resin without coagulation into large agglomerates that cannot
be readily coated onto the die surfaces. Furthermore, the process
aid must be capable of forming an adhering layer under the
extrusion conditions of temperature and pressure in order to form a
slip surface on the polymer-contacting regions of the die. In
contrast to the teachings of the prior art, the process aid need
not necessarily be above its crystalline melting point or glass
transition temperature at the process temperature, so long as it is
capable of forming a slip layer at the die surface under the shear
stress conditions generated in the extrusion, controlled by the
viscosity of the difficultly-melt-processible polymer, the
extrusion rate and the prevailing temperature. Thus, certain
melt-processible polymers and copolymers of tetrafluoroethylene
having melting points as much as 40.degree.-130.degree. C. higher
than the process temperatures are good process aids when all other
requirements are met. It is also important that the fluoropolymer
process aid be thermally and chemically stable at the melt
processing temperature of the polymer resin.
On the other hand, standard, commercially available high molecular
weight non-melt-processible polytetrafluoroethylene homopolymers,
whether dispersion-produced or suspension-produced, are not
film-forming under extrusion conditions and, therefore, are not
within the scope of this invention.
The fluoropolymer process aid of this invention should have a high
fluorine content, such that the fluorine to carbon ratio is at
least 1:2, preferably at least 1:1.5, so that the die-coating film
will have a low critical surface energy. Resultantly, there is
little wetting of the fluoropolymer by the
difficultly-melt-processible resin, and the coated die surface is
thereby rendered less resistant to the flow of the polymer
melt.
Finally, it has now surprisingly been discovered that it is
essential that the fluoropolymer have an effective amount of polar
functionality to bond the process aid to the metal or metal oxide
die surface through chemical and/or physical interaction. Suitable
polar groups include sulfonic or carboxylic groups of the type
disclosed hereinbelow, and may be situated on the polymer chain
ends as a result of the polymerization procedure or by a
post-polymerization treatment step, or they may be randomly located
along the polymer chain as part of a polar-group-containing
copolymerized monomer.
For example, copolymers of tetrafluoroethylene and
hexafluoropropylene having high concentrations of polar polymer
chain end groups are excellent process aids for
difficultly-melt-processible resins (see Example 1). These polymers
are prepared in aqueous polymerization systems using inorganic
peroxide initiators that provide --COOH or --COF polymer chain end
groups. In contrast, when such polar end groups are removed by a
humid heat treatment in isolation, as is common in commercial
practice, as disclosed in U.S. Pat. No. 3,085,083, or by a
fluorination reaction, as disclosed in U.S. Pat. No. 4,742,122,
these compositions no longer function as effective process aids
(see Comparative Examples 1 and 2).
Accordingly, the fluoropolymer process aids of this invention are
defined as those that have a molecular weight of at least 10,000,
have a fluorine to carbon ratio of at least 1:2, preferably at
least 1:1.5, are capable of forming a slip layer coating at the die
surface and have chain ends bearing one or more functional groups,
W, wherein W is selected from --COF, --SO.sub.2 F, --OSO.sub.3 M,
--SO.sub.3 M, --COOR and --COOM, wherein R is a C.sub.1-3 alkyl
group, and M is hydrogen, a metal cation, preferably an alkali or
alkaline earth metal cation, or a quaternary ammonium cation. The
concentration of the functional group, W, should be at least 100
groups per million carbon atoms (pmc), preferably at least 200
groups pmc. It may be advantageous to use in combination more than
one of the process aids of the invention. As already recited
hereinabove, the concentration of the process aid in the
difficultly-melt-processible polymer is 0.002-0.5 wt. %, preferably
0.01-0.2 wt. %.
In one important embodiment of this invention, the fluoropolymer
process aid is a homopolymer or copolymer of tetrafluoroethylene
having a high concentration of polar functional polymer chain end
groups that are introduced as a consequence of the polymerization
method employed. Such polymers include the following:
melt-processible, partially crystalline copolymers of
tetrafluoroethylene and 2-20 mole % of at least one perfluoroolefin
of 3 to 8 carbon atoms, preferably hexafluoropropylene, prepared,
for example, according to U.S. Pat. No. 2,946,763, preferably
without a buffer to ensure the presence of --COOH end groups;
partially crystalline copolymers of tetrafluoroethylene and
perfluoro(alkyl vinyl ether), preferably the propyl vinyl ether,
prepared, for example, by an aqueous process according to U.S. Pat.
No. 3,635,926 and having, for the most part, --COOH end groups, or
by a non-aqueous process, for example, according to U.S. Pat. No.
3,642,742 and having, for the most part, --COF end groups, the
disclosures of all of which are incorporated herein by reference.
The concentrations of --COF and --COOH groups in such polymers can
be measured by the infrared method described hereinbelow.
As used herein, the term "partially crystalline" means that the
fluoropolymer is melt processible, and has a crystalline melting
point above room (ambient) temperature, as distinguished from the
uncured fluoroelastomers described below, which will normally have
melting points or glass transition temperatures below room
(ambient) temperature. Such elastomers are often available as
articles of commerce. It is to be understood that small changes of
the monomer ratios in such polymers may cause them to have
crystallinity that prevents their utility as elastomers, without
detracting from their utility as fluoropolymers in the compositions
and processes of this invention.
Uncured fluoroelastomers having utility as process aids in the
invention include elastomeric copolymers of vinylidene fluoride and
one or more fluorine-containing comonomers. Such fluoroelastomers
are exemplified by the following: copolymers of vinylidene fluoride
and a monomer selected from hexafluoropropylene,
chlorotrifluoroethylene, 1-hydropentafluoropropylene and
2-hydropentafluoropropylene; copolymers of vinylidene fluoride,
tetrafluoroethylene and hexafluoropropylene or 1- or
2-hydropentafluoropropylene; and copolymers of vinylidene fluoride,
hexafluoropropylene and a perfluoro(alkyl vinyl ether). Such
copolymers can be prepared in aqueous emulsion polymerization
systems using inorganic initiators, such as described in U.S. Pat.
Nos. 2,986,649 and 3,051,677. Other useful fluoroelastomers include
perfluoroelastomers comprised of tetrafluoroethylene and a
perfluoro(alkyl vinyl ether), preferably perfluoro(methyl vinyl
ether), such as are disclosed in U.S. Pat. Nos. 3,132,123 and
4,281,092. Elastomeric copolymers of tetrafluoroethylene and
propylene, optionally with a small amount of vinylidene fluoride,
also have utility herein.
Fluoropolymer elastomers that are prepared in aqueous emulsion
polymerization systems will have predominantly --OSO.sub.3 H and
--COOH polymer chain end groups, when thermal initiation is
employed, as well as --SO.sub.3 H end groups, when redox initiation
systems are used. (See Logothetis, Prog. Polym. Sci., Vol. 14, pp
257,258 [1989]). The emulsions can be coagulated by addition of
salts, such as sodium chloride, magnesium sulfate or aluminum
sulfate, and depending on the pH during isolation, the free acids
may be present in admixture with their corresponding metal
salts.
In a further embodiment of the invention, the fluoropolymer process
aid can comprise a tetrafluoroethylene homopolymer or a copolymer
of tetrafluoroethylene and a perfluoro monomer selected from
hexafluoropropylene and a perfluoro(alkyl vinyl ether), that has
been subjected to sufficient ionizing radiation, for example, by a
method such as disclosed in U.S. Pat. No. 3,766,031, to provide the
end groups necessary to achieve the beneficial effects of the
invention. It has been found that this may be achieved by
employing, for example, 8-80 megarads, preferably 15-80 megarads,
of ionizing radiation. Such treatment generates both --COF and
--COOH groups, usually accompanied by at least some backbone
scission and reduction in molecular weight. If such ionizing
radiation treatment results in substantial crosslinking, the
crosslinked fluoropolymer is less desirable as a process aid and,
if crosslinking is extensive, it may be inoperable in this
invention.
In yet another important embodiment of the invention the
fluoropolymer process aid with polymer chain end groups can
comprise a copolymer of tetrafluoroethylene and 0.5-40 mole %,
preferably 4-40 mole %, of a functional-group-containing monomer
##STR2## wherein Z is --F or --CF.sub.3, x is 0 or an integer of
1-4, y is 0 or 1, z is an integer of 1-12, and W' is --SO.sub.2 F,
--SO.sub.2 Cl or --COOR, wherein R is C.sub.1-3 alkyl, such as are
described in U.S. Pat. Nos. 3,282,875, 3,506,635, 3,718,627,
4,065,366, 4,138,426, 4,178,218, 4,487,668 and British Patents
2,053,902, and 1,518,837 or wherein W' is --SO.sub.3 H or --COOM
wherein M is hydrogen, a metal cation, preferably an alkali metal
cation or a quaternary ammonium cation, for example,
tetraalkylammonium, and is derivable from the alkyl halides and
esters by acid or base hydrolysis. In preferred compositions of
this embodiment Z is --CF.sub.3, x: and y are each 1, z is 1-5,
preferably 2, and W' is --SO.sub.2 F, --CO.sub.2 CH.sub.3,
--SO.sub.3 H or --COOM.
Examples of difficultly-melt-processible polymers that are within
the purview of the compositions and processes of the invention
include but are not limited to mono-olefin polymers; vinyl aromatic
polymers, such as polystyrene; copolymers of alpha-olefins,
particularly ethylene, and one or more monomers selected from vinyl
esters, such as vinyl acetate or vinyl propionate, (meth)acrylic
esters, such as ethyl or methyl acrylate, (meth)acrylic acids and
their (ionomeric) metal salts, and acrylonitrile; chlorinated
polyethylene; polyvinyl chloride; polyamide; and polyester. Blends
or alloys of the above difficultly-melt-processible polymers may
also be employed in the compositions and processes of the
invention. As used herein, the term "alloy" is intended to describe
compositions obtained by melt compounding of polymeric components
containing co-reactive functional groups. As an example of such an
alloy is an alloy comprised of a polyamide 6/6, an ethylene/n-butyl
acrylate/methacrylic acid copolymer and an ethylene/n-butyl
acrylate/glycidyl methacrylate copolymer.
When the difficultly-melt-processible polymer is a hydrocarbon
polymer that is used, for example, in blown film extrusion, it will
generally have a melt index (ASTM D-1238) at 190.degree. C. of 5 or
less, preferably 3 or less. For high shear melt processing, such as
fiber extrusion or injection molding, even higher melt index
resins, for example, having a melt index of 20 or more, may suffer
extrusion difficulties.
In the case of a hydrocarbon polymer, it may comprise an
elastomeric copolymer of ethylene and propylene and, optionally, a
non-conjugated diene monomer, for example, 1,4-hexadiene, or, in
general, any thermoplastic hydrocarbon polymer obtained by the
homopolymerization or copolymerization of a monoolefin(s) of the
formula CH.sub.2 .dbd.CHR', wherein R' is H or an alkyl radical,
usually of not more than eight carbon atoms. In particular, this
invention is applicable to the following: polyethylene, both of the
high density type and the low density type having densities within
the range 0.89 to 0.97; polypropylene; polybutene-1;
poly(3-methylbutene); poly(methylpentene); and linear low density
copolymers of ethylene and an alpha-olefin such as propylene,
butene-1, hexene-1, octene-1, decene-1, octadecene and
4-methylpentene-1.
Difficultly-melt-processible polyesters are condensation polymers
derived from dicarboxylic acids and dialcohols and/or from
hydrocarboxylic acids or the corresponding lactones, such as
polyethylene terephthalate, polybutylene terephthalate and
poly-1,4-dimethylolcyclohexane terephthalate.
Difficultly-melt-processible polyamides and copolyamides are
derived from diamines and dicarboxylic acids and/or amino
carboxylic acids or the corresponding lactams, such as polyamide 6,
polyamide 6/6, polyamide 6/10, polyamide 11 and polyamide 12.
As mentioned above, it will be recognized by those skilled in the
art that for those resins that extrude at high temperatures and, in
addition, are chemically sensitive, for example polyester or
polyamide, it is important to select fluorocarbon process aids that
are thermally and chemically stable at the process temperatures.
Generally speaking, such polymers are those that are very nearly
perfluorinated, such as homopolymers of tetrafluoroethylene or
copolymers of tetrafluoroethylene and other perfluoroolefins.
Copolymers of vinylidene fluoride and hexafluoropropylene, for
example, may dehydrohalogenate at temperatures in excess of about
250.degree. C. and are of lesser utility under these
conditions.
The invention is also applicable to difficultly-melt-processible
polymers containing pigments and antiblock agents, such as silica,
clays and glass beads. Light stabilizers, antioxidants and other
common additives may also be incorporated therein.
Because of the different extrusion characteristics of the various
polymers operable herein, the utility of the process of this
invention may be of greater value with some polymers than with
others. Thus, for example, hydrocarbon polymers, such as
polypropylene or branched polyethylene, that are not of high
molecular weight, have good melt flow characteristics even at low
temperatures, so that surface roughness and other surface defects
can be avoided by adjustment of extrusion conditions. Such
hydrocarbon polymers may not require the use of the process aid of
this invention, or be noticeably improved by it, except under
unusual, adverse extrusion conditions. However, other polymers,
such as high molecular weight, high density polyethylene or linear
low density polyethylene copolymers, and high molecular weight,
polypropylene and propylene/alpha-olefin copolymers, particularly
those with narrow molecular weight distributions, do not have this
degree of freedom in the variation of extrusion conditions and it
is particularly with these resins that remarkable reductions in
extrusion pressure and/or improvements in the surface quality of
the extruded product are obtained by the composition and process of
the invention.
Although not wishing to be bound by the following, it is postulated
that there is an interaction, chemical and/or physical, between the
polar end groups or midchain polar structures, if present, and the
polymer-contacting metal surfaces of the extruder, particularly
within the die land area, thus causing the formation of an adherent
die-coating layer of low surface energy fluoropolymer; and that
bonding or attraction between polymer and metal occurs at
metal-oxygen bonds on the die surfaces.
It will be recognized by one skilled in the art that it may not be
possible to achieve, simultaneously, reduced die pressure,
increased throughput and improved surface quality to the maximum
extent at a given concentration of fluoropolymer process aid. Thus,
one might elect to attain maximum improvement in one parameter at
the expense of corresponding improvements in other parameters. For
example, increased output of extrudate with high quality surface
characteristics may not necessarily be accompanied by reduced die
pressure. Similarly, in some systems substantial reductions in
operating die pressures are achieved, but without significant
improvements in extrudate surface qualities. Reductions in pressure
fluctuations or elimination of die buildup may be achieved, but
without further improvements in surface quality. Alternatively, and
for matters of operating economies, it may be desirable to operate
at very low levels of fluoropolymer process aid rather than to
achieve the maximum improvements in extrusion parameters achievable
at higher concentrations. The best set of conditions will be
determined by the specific requirements of the extrusion.
The addition of the fluorocarbon polymer process aid to the
difficultly-melt-processible polymer can be accomplished by any of
the means heretofore developed for the addition of modifiers to
such polymers. The fluorocarbon polymer may be added, for example,
to a hydrocarbon polymer on a rubber compounding mill or in a
Banbury or other internal mixer or in a mixing extruder. When the
fluoropolymer process aid is a non-massing powder, it is also
feasible to dry-blend the fluoropolymer process aid with the host
polymer in the solid state, and then effect uniform distribution of
the fluoropolymer in the melt extruder employed in the fabrication
by using an extruder screw with good mixing capability.
Alternatively, in some cases, masterbatch dispersions of the
fluoropolymer process aid in a diluent polymer can be metered to
the feed section of the extruder by appropriate devices or
dry-blended with the host polymer prior to extrusion. Exceptions to
this practice may apply with fluoropolymer process aids that are
not necessarily melted at extrusion process temperatures. When such
process aids are heated to higher temperatures in the
masterbatch-forming process, under which conditions fluoropolymer
particles may coalesce to larger particles, they are not
appropriately subdivided in the final extrusion of the
difficultly-melt-processible polymer. The diluent polymer can be a
difficultly-melt-processible polymer, or it can be a
melt-processible polymer that does not substantially deleteriously
affect the interaction of the aforesaid fluoropolymer process aid
with the metal surfaces of the extrusion die. For example, when the
difficultly-melt-processible polymer is linear low-density
polyethylene, the diluent polymer can be a melt-processible
hydrocarbon polymer, such as a homopolymer or copolymer of a
monoolefin(s) of the formula R'CH.dbd.CH.sub.2 wherein R' is H or
an alkyl radical, usually of not more than eight carbon atoms.
In the practice of this invention, it will be found that the
beneficial effects in the reduction of extruder die pressures and
improvement in the rates of extrusion that may be employed without
encountering melt fracture are not necessarily observed immediately
on the onset of extrusion, and depending on the overall
concentrations of modifier, it may take from 10 minutes to 8 hours
to reach stable extrusion rate and die pressure. Longer times are
required at low concentrations of fluoropolymer process aid and
with process aids having lower concentrations of the functional
group W. When it is desirable to hasten the achievement of
equilibrium, it may be expedient to first "condition" the extruder
rapidly using a composition containing 0.5-2 parts of the fluoro
polymer and then to switch to the desired lower concentration of
process aid.
The concentration of the polar functional groups in the
perfluoropolymer process aid of the invention may be determined
from the infrared spectrum of compression-molded films, according
to the technique described in U.S. Pat. Nos. 4,742,122 and
3,085,083, as follows:
The quantitative measurement of the number of end groups is
obtained using the absorptivities measured on model compounds
containing the end groups of interest. The end groups of concern,
the wavelengths involved, and the calibration factors determined
from model compounds are shown below:
______________________________________ Wavelength, Calibration
Factor End group micrometers (CF)
______________________________________ --COF 5.31 406 --CO.sub.2
H(M) 5.52 335 --CO.sub.2 H(D) 5.64 320 --CO.sub.2 CH.sub.3 5.57 368
--CONH.sub.2 2.91 914 --CF.dbd.CF.sub.2 5.57 635 --CH.sub.2 OH 2.75
2220 ______________________________________ (M) = Monomeric, (D) =
Dimeric
The calibration factor is a mathematical conversion to give end
group values in terms of ends per 10.sup.6 carbon atoms. The
concentration of each type of end in a polymer film may generally
be obtained from this equation: ##EQU1## where film thickness is in
millimeters.
Some of the absorbance peaks may interfere with one another when
--CO.sub.2 H(D), --CO.sub.2 H(M), and --CF.dbd.CF.sub.2 ends are
all present. Corrections have been developed for the absorbances of
--CO.sub.2 H(D) (hydrogen-bonded carboxylic acid dimer) and the
--CF.dbd.CF.sub.2 ends. These are as follows (where .mu. is the
wavelength in micrometers): ##EQU2## the corrected absorbance for
--CO.sub.2 H(D) ##EQU3## the corrected absorbance for
--CF.dbd.CF.sub.2
The presence of --CONH.sub.2 or --CO.sub.2 CH.sub.3 may also
interfere with the acid and --CF.dbd.CF.sub.2 absorbances. Since
these groups are generally the result of additives to
polymerization, their presence is generally predictable. A
suspicion of --CONH.sub.2 absorbance in the vicinity of 5.6
micrometers can be checked by searching for the auxiliary
--CONH.sub.2 band at 2.91 micrometers.
The polymer films (0.25 to 0.30 mm thick) are scanned on a
Perkin-Elmer 283B spectrophotometer with a film of the same
thickness, and known to contain none of the ends under analysis, in
the instrument reference beam. The instrument is set up with a
Response Time setting of 1, a Scan Time setting of 12 minutes,
Ordinate Expansion of 2, a Slit Program of 7, and an Auto-Chek Gain
control of 20%. The films are then scanned through the pertinent
regions of the spectrum making sure that adequate base lines are
established on each side of the pertinent absorbances.
The polymer films are generally compression molded at
270.degree.-350.degree. C. The presence of certain salts,
particularly alkali metal salts, may cause end group degradation
within this temperature range. If these salts are present, the
films should be molded at the lowest possible temperature.
Note that this method is calibrated for use with perfluoropolymers.
If the carbon to which the functional group is attached contains
hydrogens, there will be some shifts in absorption wavelengths and
calibration factors, as will be apparent to those skilled in the
art.
EXAMPLES
Examples 1-8 that follow were carried out with a C. W. Brabender
Instruments, Inc. Computerized Plasti-Corder equipped with a 19.1
mm. (3/4 in.) diameter extruder with a 25/1 length/diameter ratio.
The chromium plated screw had ten feed flights, 10 compression
flights with a compression ratio of 3:1, and 5 metering flights.
Operating parameters were controlled by four or five independent
heating zones, depending on the die, two pressure transducers and a
torque-measuring drive unit with 1-120 rpm capability. The
instrument was equipped with software for rheometric extrusion
testing. One of two die assemblies was used, as noted in the
examples, a standard nitrided #416 stainless steel capillary die
with a diameter of 2 mm. and L/D of 20, or a horizontal ribbon
(tape) die body made of #416 ferritic stainless steel, supplied by
C. W. Brabender and designed to accept chromium plated die inserts
such that the exit width was 2.54 cm. (1.0 in.), the land length
was 1.016 cm. (0.4 in.) and the die gap was a nominal 0.508 mm.
(0.02 in.). The various new die inserts were used as received after
wiping with ScotchBrite.RTM. scouring pads and acetone to remove
surface contaminants.
In operation, the required machine conditions were set and the
polymer resin then extruded, usually at 40 rpm when using the
capillary die, and 60 rpm when using the tape die, until
equilibrium (constant throughput and constant die pressure) was
reached. Experiments were carried out in a sequence of unmodified
resin, followed by resin containing fluoropolymer process aid. When
changing the feed composition, the initial output parameters
corresponded to the previous equilibrium, and then gradually
changed to a new equilibrium. In some of the examples that follow,
when switching from unmodified hydrocarbon polymer to the blend
containing fluoropolymer process aid, a "conditioning" operation
using a 1% blend of fluoropolymer process aid was first used for 30
min. to speed the attainment of equilibrium, and then the feed was
switched to a blend containing the desired test concentration of
fluoropolymer process aid. Equilibrium was achieved for each
composition, and a range of screw speeds was run to produce new
equilibrium values of throughput and die pressure. Surface quality
of the extrudate was judged by visual examination.
After each series of examples the die inserts were removed, and the
die body and extruder were purged with one of several materials,
such as PCX-12 purge compound (available from Du Pont Canada), Du
Pont 3535 polyethylene 1 melt index linear low density polyethylene
(LLDPE), or LLDPE containing 20% silica. Replacement die inserts
were installed. After calibration of the transducers, the
unmodified resin was run to establish equilibrium conditions, and
to assure that reliable output was being obtained. If previously
established equilibrium values for unmodified resin were not
achieved, the cleanout procedure was repeated. Because combinations
of small amounts of fluoroelastomer and fluororesins can act
synergistically, the extruder was cleaned extremely well following
any use of fluoroelastomer using the following procedure. The
extruder and die body were purged as above and then completely
disassembled. The screw, barrel, die assembly, transducers and
thermocouples were thoroughly cleaned, first with a motor driven
brass brush, and finally with acetone solvent. An extrusion test
for equilibrium parameter values was then carried out as described
above.
The linear low density polyethylene, LLDPE, used in the following
examples was a high molecular weight, linear low density (d=0.918)
copolymer of ethylene and butene-1 having a melt index (ASTM
D-1238, cond. E) of 1.0.
Example 1
(A) To the extruder, equipped with a capillary die, was fed
unmodified LLDPE with the screw operating at 40 rpm and heating
zones No 1-5 controlling at nominal temperature settings of 150,
180.degree., 200.degree. and 204.degree. and 205.degree. C.,
respectively. Equilibrium extrusion conditions, where throughput
and die pressure were constant, were reached after a period of 30
min. The screw speed was then systematically varied from 20 rpm to
120 rpm. After determining the extrusion rate at various screw
speeds, the data were used to generate a curve of die pressure vs.
throughput such as is shown in FIG. 1 as Curve 1. Surface
appearance of the die strand was evaluated visually. Melt fracture
occurred at all extrusion rates in excess of 8 g./min., the lowest
rate attainable on the equipment. For purposes of comparison, "melt
fracture" is defined as a herringbone-like roughness on the surface
of the extrudates.
(B) Without changing conditions, the extruder feed was changed to a
blend containing 0.05 wt. % (500 ppm) of a copolymer (FEP) of
tetrafluoroethylene and 12 wt. % of hexafluoropropylene having a
melt viscosity of 10.3.times.10.sup.4 poise and a DSC melting point
maximum in the range 250.degree.-280.degree. C. It was in a powder
form, prepared without humid heat treatment during isolation. By
infrared analysis it was shown to contain approximately 420
carboxyl end groups per million carbon atoms and had essentially no
--COF end groups. The die pressure decreased gradually, and after a
total time of 120 min. following the switch to fluoropolymer blend,
a new equilibrium was established. Extrusion was continued without
any further die pressure changes, and after a total extrusion time
of 210 min., a plot of die pressure vs. extrusion rate was
generated as shown in FIG. 1, Curve 2. Melt fracture did not occur
up to a maximum extrusion rate attainable of 52 g/min.
Comparative Example 1
A portion (50 g) of an FEP polymer powder similar to that used in
Example 1 was placed in a chamber which was evacuated, purged with
nitrogen, and then heated to 95.degree. C. The chamber was again
evacuated and pressured back up with nitrogen, evacuated again and
then pressured back up with a 25/75 volume mixture of
fluorine/nitrogen gases. The temperature was allowed to rise to
100.degree. C. and the same gas mixture was passed through the
reactor at 0.9 L/min. for 2 hrs. The temperature was raised to
185.degree. C. while maintaining the same gas flow. After 1 hr. at
185.degree. C. the gas flow rate was decreased to 0.7 L/min. The
fluorine/ nitrogen flow was maintained at this level for 4 hrs.
after the temperature was raised to 185.degree. C. The total amount
of fluorine passed through the reactor was calculated from the
cylinder pressure change to be 0.8 gram per gram of polymer. The
chamber was then purged with nitrogen, cooled to room temperature,
and opened to obtain the treated polymer. The treated polymer was
cold pressed into a film which was scanned by Infrared
Spectroscopy. Using known IR absorptivities for --COF and --COOH
structures in fluoropolymers, it was determined that the treated
polymer contained 14 --COF ends per million carbon atoms and no
--COOH ends. It had a melt viscosity of 9.94.times.10.sup.4
poise.
LLDPE containing no fluoropolymer additive was extruded as
described in Example 1, giving essentially equivalent results.
Extrusion of LLDPE containing intimately blended therein 500 ppm of
the above fluorine-modified FEP polymer was carried out as in
Example 1. There was no drop in die pressure when the modified FEP
was introduced, as shown by curve 3 in FIG. 1, and there was no
improvement in melt fracture behavior compared to the unmodified
LLDPE (curve 1).
Comparative Example 2
An FEP polymer was prepared in a fashion similar to that used in
the preparation of the FEP sample of Example 1, except that it was
subjected to a humid heat treatment in isolation, as described in
U.S. Pat. No. 3,058,083. It had a melt viscosity of
7.8.times.10.sup.4 poise and by infrared analysis had no detectable
end groups. A blend of 1000 ppm of this polymer in LLDPE was
evaluated as described in Example 1. There was no reduction in die
pressure or improvement in melt fracture behavior for the blend,
relative to the LLDPE not containing this fluoropolymer.
Comparative Example 3
This experiment was carried out as described in Example 1, except
the tape die assembly was used and the four heating zones were
controlled at 150.degree., 180.degree., 200.degree. and 204.degree.
C., respectively. Using LLDPE not containing fluoropolymer process
aid, the Control reference data shown in FIG. 2 as Curve 1 were
obtained as described in Example 1.
Comparative Example 4
Using the procedures of Comparative Example 3 a blend of LLDPE
containing 1000 ppm of intimately dispersed, commercially
available, dispersion-process-polymerized, fibrillatible,
non-melt-processible polymer of TFE containing a small amount of
copolymerized hexafluoropropylene was evaluated; end group
functionality was immeasurably low. There was no reduction in
extruder die pressure or improvement in melt fracture behavior.
Example 2
Using the procedure of Comparative Example 3 a blend of LLDPE
containing 1000 ppm of a molecular weight, dispersion-produced
PTFE, that had been subjected to 60 megarads of ionizing radiation
and had 650 --COF and 1235 --COOH end groups per million carbon
atoms and a DSC melting point of 321.degree. C., was evaluated.
There was a significant reduction in extruder die pressure,
compared to the control, as shown in FIG. 2, Curve 2, and melt
fracture occurred only at extrusion rates above 42 g/min.
Example 3
Using the procedure of Comparative Example 3 a blend of LLDPE
containing dispersed therein 200 ppm of a copolymer of
tetrafluoroethylene and 13.2 mole % of
perfluoro-3,6-dioxa-4-methyl-7-octene sulfonic acid (Aldrich
Chemical Co., Cat. No. 27673-1) was evaluated. The plot of die
pressure vs. extrusion rate is shown in Curve 2 of FIG. 3 and is
compared with the unmodified LLDPE control, Curve 1, which was
generated in Comparative Example 3. Melt fracture had not occurred
at extrusion rates of 48 g/min., the maximum extrusion rate
achievable.
Example 4
Using the procedure of Comparative Example 3 a blend of LLDPE
containing 200 ppm of the tetrafluoroethylene copolymer of Example
3 and 200 ppm of an FEP copolymer similar to that of Example 1, but
having 456 --COF and --COOH end groups per million carbon atoms and
a melt viscosity of 8.95.times.10.sup.4 poise, was evaluated.
Extrusion data are shown in Curve 3 of FIG. 3. Melt fracture had
not occurred at an extrusion rate of 49 g/min., the maximum rate
achievable.
Example 5
In a procedure like that of Comparative Example 3 a blend of LLDPE
containing 400 ppm of a copolymer of tetrafluoroethylene and 13.7
mole % methyl perfluoro(4,7-dioxa-5-methyl-8-noneneoate) and 100
ppm of the FEP copolymer of Example 4 was evaluated. Extrusion data
are shown as Curve 4 in FIG. 3. Melt fracture did not occur at
extrusion rates below 48 g/min., the maximum rate achievable.
Example 6
In a procedure like that of Comparative Example 3 a blend of LLDPE
containing 1000 ppm of a copolymer of tetrafluoroethylene and
perfluoro-3,6-dioxa-4-methyl-7-octene sulfonyl fluoride was
evaluated. The plot of die pressure vs. extrusion rate is shown in
Curve 5 of FIG. 3. No melt fracture was observed up to the maximum
extrusion rate tested, 53 g/min.
Example 7
A terpolymer having principally sulfonic end groups was prepared in
a 4L mechanically agitated, water-jacketed, stainless steel
autoclave operating continuously at 70.degree. C. and 4800 kPa,
into which was pumped, at a rate of 500 mL/h, an aqueous
polymerization medium/initiator solution comprised of 500 mL water
and 6.7 g sodium sulfite and, at a rate of 600 mL/h, another
aqueous solution comprising 600 mL water, 7.5 g ammonium persulfate
and 15 g ammonium perfluorooctanoate. At the same time,
tetrafluoroethylene (250 g/h), perfluoro(methyl vinyl ether) (325
g/h) and perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) (8CNVE,
14.4 g/h) were fed to the autoclave as a compressed mixture at a
constant rate by means of a liquid pump. Polymer latex was removed
continuously by means of a let-down valve and unreacted monomers
were vented. The latex, from about 5 hrs. operation, was added with
stirring to a preheated (90.degree. C.) coagulating solution
consisting of 230 g magnesium sulfate in 25 L water. The coagulated
crumb was filtered off, washed repeatedly with water and dried by
heating in an air oven at 80.degree. C. for 48 hrs. to give about
2300 g of polymer. The polymer composition (wt %) was 63% TFE, 35%
PMVE and 2% 8CNVE as determined by infrared analysis.
In a procedure like that of Example 1 a blend of LLDPE containing
1000 ppm of the above-prepared fluoropolymer was evaluated.
Extrusion data are shown by Curve 2 of FIG. 4 and are compared with
data for LLDPE containing no fluoropolymer process aid in Curve 1.
Melt fracture did not occur at extrusion rates below 52 g/min., the
maximum rate achievable.
Example 8
A terpolymer having principally carboxyl end groups was prepared in
a 4L mechanically agitated, water-jacketed, stainless steel
autoclave operating continuously at 90.degree. C. and 4800 kPa,
into which was pumped, at the rate of 1500 mL/h, an aqueous
polymerization medium/initiator solution comprising 1500 mL water,
3.85 g ammonium persulfate, 22 g of ammonium perfluorooctanoate
("Fluorad" FC-143, 3M Co.) and 22 g disodium hydrogen phosphate
heptahydrate (Na.sub.2 HPO.sub.4.7H.sub.2 O). At the same time,
tetrafluoroethylene, TFE, (465 g/h), perfluoro(methyl vinyl ether),
PMVE, (480 g/h) and vinylidene fluoride, VF.sub.2, (3.0 g/h) were
fed to the autoclave at a constant rate by means of a diaphragm
compressor. Polymer latex was removed continuously by means of a
let-down valve and unreacted monomers were vented. The latex, from
about 4 hrs. operation, was added with stirring to a preheated
(90.degree. C.) coagulating solution consisting of 320 g magnesium
sulfate in 25 L water. The coagulated crumb was filtered off,
washed repeatedly with water and dried by heating in an air oven at
80.degree. C. for 48 hrs. to give abut 3200 g of polymer. The
polymer composition (wt %) was 64.8% TFE, 34.8% PMVE and 0.4%
VF.sub.2 as shown by infrared analysis.
In a procedure like that of Example 1 a blend of LLDPE containing
1000 ppm of the above-described fluoropolymer was evaluated.
Extrusion data are shown by Curve 3 of FIG. 4. Melt fracture did
not occur at extrusion rates below 42 g/min., the maximum rate
achievable.
Comparative Example 5
In a procedure like that of Comparative Example 3, a blend of LLDPE
and 1000 ppm of a commercially available (Du Pont Company)
powdered, essentially alternating copolymer of tetrafluoroethylene
and ethylene. It had a DSC melting maximum in the range of
250.degree. C. Although acid or acid fluoride end groups of this
fluoropolymer were is very low because of the high hydrocarbon
concentration and the method of polymerization of the polymer (see
U.S. Pat. No. 3,624,250). There was no die pressure drop relative
to that of the LLDPE containing no fluoropolymer process aid, and
melt fracture occurred at all extrusion rates above 16 g/min., the
minimum rate tested.
Example 9
The equipment employed was a Haake Buchler Rheomix.RTM. 19.1 mm
(3/4 in.) diameter single-screw extruder with a chromium plated
one-stage metering screw having a 20/1 length/diameter ratio, 10
feed flights, 5 compression flights, 5 metering flights and a
channel depth ratio of 3. Operating parameters were controlled by
four independent heating zones, two pressure transducers and a
torque-measuring drive with 1-200 rpm capability. The extruder was
equipped with software for rheometric capillary extrusion testing.
The capillary die, made from #416 stainless steel, had a diameter
of 1.27 mm and a length of 39.1 mm and was previously unused. Prior
to each use the extruder was thoroughly cleaned by first purging
with linear low density polyethylene containing 20% silica. The
extruder was then disassembled and each section was cleaned with a
wire brush and then methyl ethyl ketone solvent. The die holder was
cleaned by heating at 600.degree. C. for 4 hrs.
(A) A commercially available extrusion grade polystyrene,
Styron.RTM. 685D (Dow Chemical Co.), density 1.40 g/cc, melt flow
rate 1.6 g/10 min., was fed to the extruder, equipped with a new
die, with the screw operating at 5 rpm and heating zones 1, 2, 3,
and 4 controlled at nominal settings of 150.degree., 180.degree.,
200.degree. and 204.degree. C., respectively (No. 4 is closest to
the die). Equilibrium extrusion conditions were achieved after 120
min. The screw speed was then systematically varied from 1 rpm to
120 rpm to generate, as previously described, the correlation of
extruder throughput and die pressure shown in Curve 1 of FIG. 5.
Melt fracture was not observed at any screw speed tested, but die
buildup (collection of polymer at the exit of the capillary die)
was observed at screw speeds greater than 60 rpm.
(B) Without changing conditions the feed was changed to a powder
blend of polystyrene containing 0.05 wt. % of the irradiated PTFE
described in Example 2. Using the procedure of Part A, a new
equilibrium was established after 240 min., and the data of Curve 2
of FIG. 5 was generated. Die buildup was not observed at any screw
speed.
Example 10
In a procedure like that of Example 9, except t hat the extruder
heating zones Nos. 1, 2, 3 and 4 were controlled at nominal
temperature settings of 160.degree., 180.degree., 220.degree. and
220.degree. C., respectively, the performance of an extrusion grade
ethylene/vinyl acetate copolymer (Du Pont Elvax.RTM.-3135), density
0.930 g/cc, melt index of 0.35 g/10 min., was evaluated. Curve 1 of
FIG. 6 shows data for extrusion of unmodified EVA polymer. Curve 2
shows data for extrusion of a blend containing 0.05 wt. % cf a
copolymer similar to that of Example 8 but comprised of 55.4 wt. %
of tetrafluoroethylene, 44.2 wt. % perfluoro(methyl vinyl ether)
and 0.4 wt. % vinylidene fluoride.
Example 11
(A) In a procedure like that of Example 9, except that the extruder
heating zones Nos. 1, 2, 3 and 4 were controlled at nominal
temperature settings of 280.degree., 310.degree., 310.degree. and
310.degree. C., respectively, the performance of an extrusion grade
PET copolymer of ethylene glycol and terephthalic acid (Goodyear
Co.), density 1.39 g/cc, inherent viscosity (0.05 wt. % in a 3/1
mixture of methylene chloride and trifluoroacetone)1.65, was
evaluated. Die pressure was measured at a constant screw speed of 5
rpm over a period of 120 min. The die pressure fluctuated steadily
between about 3 to 10 MPa over a timer period of several minutes.
After 120 min. the screw speed was varied from 1 to 30 rpm. Large
die pressure fluctuations continued and at 30 rpm caused automatic
shutoff of the extruder which had a safety cutoff pressure set at
70 MPa. At 30 rpm flow rate was 19.8 g/min. Thus, the PET could not
be extruded at screw speeds greater than 30 rpm or at a flow rate
greater than 19.8 g/min. In addition, an accumulation of dark
decomposed polymer was observed to build up at the exit of the
capillary die at all extrusion speeds.
(B) Without changing conditions, the extruder feed was changed to a
powder blend of the PET containing 0.05 wt. % of the
fluoroelastomer described in Example 10. After several minutes at 5
rpm the large pressure fluctuations observed above abruptly ceased.
After 120 minutes the screw speed was varied from 1 to 60 rpm,
where the flow rate was 31.2 g/min. The pressure was steady at all
speeds and there was no accumulation of decomposed polymer at the
die exit. At 90 rpm the pressure exceeded the safety cutoff
pressure.
Example 12
(A) In a procedure like that of Example 9, except that the extruder
heating zones Nos. 1, 2, 3 and 4 were controlled at nominal
temperature settings of 260.degree., 290.degree., 297.degree. and
297.degree. C., respectively, the performance of a commercially
available extrusion grade copolymer of ethylene glycol and
terephthalic acid containing 0.25 wt. % trimellitic anhydride,
inherent viscosity (0.05 wt. % in a 3/1 mixture of methylene
chloride and trifluoroacetone) 1.05, DSC melting point 254.degree.
C., was evaluated. Die pressure was measured at a constant screw
speed of 5 rpm over a period of 120 min. The die pressure
fluctuated steadily between about 3 to 10 MPa over a time period of
several minutes. After 120 min. the screw speed was varied from 1
to 60 rpm. Large die pressure fluctuations contined at all speeds.
Above 60 rpm pressure fluctuations caused automatic shutoff of the
extruder (pressure reached 70 MPa). At 60 rmp the flow rate was
30.6 g/min. Thus, the PET could not be extruded at screw speeds
greater than 60 rpm or at a flow rate greater than 30.6 g/min.
(B) Without changing conditions the extruder feed was changed to a
powder blend of the same polyester containing 0.05 wt. % of the
carboxyl-group-containing FEP copolymer described in Example 1.
After several minutes at 5 rpm the large pressure fluctuations
observed above abruptly ceased and the die pressure became steady.
After 120 minutes the screw speed was varied from I to 90 rpm,
where the flow rate was 40.8 g/min. and the pressure was steady at
all speeds. At 120 rpm the pressure exceeded the safety cutoff
pressure.
Comparative Example 6
The procedure of Example 12 was repeated except that in Part B a
blend containing 0.05 wt. % of the FEP polymer described in
Comparative Example 2 was evaluated. The large pressure
fluctuations of Part A were not diminished in the procedure of Part
B and continued for a period of greater than 120 minutes at 5 rpm.
The screw speed was varied from 1 to 60 rpm, where die pressure
fluctuations continued at all speeds. At 60 rpm the flow rate was
26.4 g/min. At 90 rpm the pressure exceeded the safety cutoff
pressure of the extruder, 70 MPa.
Example 13
(A) In a procedure like that of Example 9 a commercially available
fiber grade nylon 66 having a relative viscosity of 43, density
1.10 g/cc (T-972; Du Pont Co.) was fed into the extruder with the
screw operating at 5 rpm and heating zones Nos. 1, 2, 3 and 4
controlled at nominal temperature settings of 260.degree.,
270.degree., 270.degree., 270.degree. C., respectively. After
steady conditions were achieved, die pressure was measured at a
constant screw speed of 5 rpm over a period of 120 minutes, during
which time the die pressure fluctuated regularly between about 4.8
to 14 MPa with a time period of several minutes. The screw speed
was then systematically varied from 1 rpm to 120 rpm. Large die
pressure fluctuations were observed at all screw speeds up to 60
rpm (flow rate of 9.6 g/min.), diminishing to about .+-.0.7 MPa at
90 and 120 rpm. Representative extrusion data are shown in FIG. 7,
Curve 1.
(B) Without changing conditions, the extruder feed was changed to a
powder blend of the nylon containing 0.05 weight percent of the
irradiated PTFE described in Example 2. After several minutes at 5
rpm the large fluctuations in die pressure observed in the
procedure of Part A ceased and the die pressure became steady, with
fluctuations of no more than .+-.0.15 MPa. Extrusion was continued
without any further die pressure change. After 120 min., the screw
speed was systematically varied from 1 rpm to 120 rpm. Die pressure
was steady at all screw speeds with fluctuations of no more than
.+-.0.15 MPa. Data are shown in FIG. 7, Curve 2.
Example 14
The evaluations reported below employed the apparatus described in
Example 9, except for using a capillary die made from #416 nitrided
stainless steel that had a diameter of 0.38 mm and a length of 0.76
mm. The die was heated in an electric furnace for 4 hours at
450.degree. C. prior to use.
(A) A commerically available fiber grade nylon 66 having a relative
viscosity of 43, density 0.10 g/cc (T-972; Du Pont Co.) was fed
into the extruder with the screw operating at 5 rpm and heating
zones Nos. 1, 2, 3 and 4 controlled at nominal temperature settings
of 260.degree., 270.degree., 270.degree. and 270.degree. C.,
respectively, (No 4 is closest to the die). After equilibrium was
achieved, screw speed was reduced to 3 rpm to achieve an extrusion
rate of 2 g/min. Die pressure at this extrusion rate was 3.1 MPa.
After a period of one hour no buildup of polymer was observed at
the exit of the die. The temperatures of heating zones 3 and 4 were
then both increased periodically in 5.degree. C. increments, up to
a temperature of 300.degree. C. In each case the extrusion speed
was adjusted to 2 g/min. by changing the rpm, and the extrusion was
continued for one hour. Whenever a die deposit was observed to
collect at the die exit, at any temperature, the die was cleaned by
wiping shortly after increasing to the next higher temperature and
adjusting the screw speed. Buildup of a ring of black decomposed
polymer first appeared at the exit of the die, around the extruding
nylon fiber, during the extrusion at 280.degree. C. Similarly, a
ring of demomposed polymer appeared at all temperatures tested
between 280.degree. and 300.degree. C.
(B) Starting conditions were returned to a screw speed of 5 rpm and
heating zones Nos. 1, 2, 3 and 4 where controlled at settings of
260.degree., 270.degree., 270.degree. and 270.degree. C.,
respectively. The extruder feed was changed to a powder blend of
nylon containing 0.05 wt. % of the same irradiated PTFE as used in
Example 2. After equilibrium was achieved, screw speed was
increased to 10 rpm to achieve an extrusion rate of 2 g/min. Die
pressure at this extrusion rate was 3.8 MPa. After a period of one
hour, no buildup of polymer was observed at the exit of the die.
The temperatures of heating zones 3 and 4 were then incrementally
increased as described in Part A. Buildup of a globule of black
decomposed polymer first appeared at the exit of the die, near the
extruding nylon fiber, during the extrusion at 285.degree. C. After
wiping the die clean, a globule of decomposed polymer appeared at
all temperatures tested between 285.degree. C. and 300.degree.
C.
(C) The procedure of Part A was repeated except that the extruder
feed was a powder blend of the nylon containing 0.05 wt. % of the
same FEP as used in Example 1. After equilibrium was achieved at a
melt temperature of 270.degree. C. and a screw speed of 5 rpm,
screw speed was held constant at 5 rpm to achieve an extrusion rate
of 2 g/min. Die pressure at this extrusion rate was 4.7 MPa. After
a period of one hour, no buildup of polymer was observed at the
exit of the die. The temperatures of heating zones 3 and 4 were
then both increased periodically in 5.degree. . increments as
described in Part A, and the extrusion speed was adjusted to 2
g/min. in each case. Buildup of a globule of black decomposed
polymer first appeared at the exit of the die, near the extruding
nylon fiber, during the extrusion at 280.degree. C. and 300.degree.
C.
(D) The procedure of Part A was repeated except that the extruder
feed was a powder blend of nylon containing 0.02 wt. % each of the
fluorocarbon polymers described in Parts B and C. After equilibrium
was achieved at a melt temperature of 270.degree. C. and a screw
speed of 5 rpm, screw speed was held constant at 5 rpm to achieve
an extrusion rate of 2 g/min. Die pressure at this extrusion rate
was 4.7 MPa. After a period of one hour, no buildup of polymer was
observed at the exit of the die. The temperatures of heating zones
3 and 4 were then both increased periodically in 5 C increments to
300.degree. C. as described in Part A. No buildup of either a ring
or globule of decomposed polymer appeared at the exit of the die
during extrusion at any temperature between 270.degree. C. and
300.degree. C., the highest temperature tested.
Example 15
In this example the extrusion of polymer alloy comprised of 50 wt.
% Zytel.RTM. 101 Nylon 6/6 (Du Pont Co.), 16 parts of a copolymer
of ethylene/n-butyl acrylate/glycidyl methacrylate (70.6/28/1.4 wt.
ratio), 36 parts of an ethylene/n-butyl acrylate/methacrylic acid
copolymer (65/25/10 wt. ratio) and containing 1 wt. % zinc stearate
and 1.5 wt. % Irganox.RTM. 109B antioxidant was evaluated. The
alloy was prepared by mixing in a twin-screw extruder at
285.degree. C., 110 rpm, followed by pelletization and then drying
to 0.15 wt. % or less of moisture. An extruder similar to that
described in Example 9 with a single hole die set at a 45 degree
exit angle was employed. With the system operating at 290.degree.
C. and polymer fed at 60 rpm, a dark ring of degraded polymer
formed around the extrudate within a few minutes after extrusion
began and slowly increased in size. Parts of the ring periodically
broke away and formation of a new ring of degraded material formed
again.
Without changing conditions a dry blend of the same alloy
containing 0.05 wt. % of the FEP polymer described in Example 1 was
fed to the extruder. The ring of degraded polymer gradually
decreased in size until after 1.25 hrs. the die face was clean and
a clean extrudate was observed The feed was then changed to a blend
of the alloy containing 0.05 wt. % of the irradiated PTFE described
in Example 2. There was an approximately 20% drop in die pressure
and the extruder die remained free of degraded polymer
deposits.
When the extruder feed was changed back to the polymer alloy not
containing a fluoropolymer additive, the die pressure increased and
a ring of degraded polymer soon formed at the die exit orifice.
Example 16
Using the polymer alloy described in Example 15 an injection blow
molding trial was carried out with the parison die nozzle regulated
at 280.degree. C. In the absence of fluoropolymer additive there
was a black die deposit buildup and deposition of the deposit onto
the parison tube. There was no die deposit or contamination of the
parison when a dry blend of the alloy containing 0.05 wt. % of the
irradiated PTFE of Example 2 was used.
* * * * *